Method and apparatus for regulating the head and capacity of centrifugal pumps



`luly 31, 1945. 1 F. MOODY 2,380,606 v METHQD AND APPARATUS FOR REGULATINCT THE HEAD AND CAPACITY OF CENTRIFUGAL PUMPS LEM/15 1:.' Mnnqy u lNv NToR in BY ATTORNEY 2 t e e h S S .Tv D h M S H 4 Tw MP I L MAZ L U ER ORT9 ORNl Mom.

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y n Y L5M/115 M009/ IN NTOR ATTORNEY July 31, 1945. A F. Moo 2,380,606

' METHOD AND APP TUS FOR R G LATING HEAD AND CAPACITY OF CE IFUGAL PU Filed 1942 ENTOR July 31, 1945. l.. F. MOODY METHOD AND APPARATUS FOR 'REGULATING THE HEA ND CAPACITY- OF GENTRIFUGAL PUMPS Filed Deo 19, 1942 4 Sheets-Sheet k4 E# ff Y @y \\\\\\\\\\\\\\\\\\\\\QW/QlnunnuA y v 1/ A Lema 1? Maa@ IN NToR v ArroRNEY Patented July 3l, 1945 METHOD AND PPARATUS FOR REGULAT- ING THE HEAD AND-CAPACITY F CEN- TRIFUGAL PUMPS Lewis F. Moody, Princeton, N. J.

Application 'December' 19, 1942, Serial No. 469,504

` (ci. s-97) Claims.

This invention reltes to centrifugal pumps and compressors and more specifically to a method and construction of pump for regulating the head and capacity of such machines. v

While the invention is particularly adaptable for use in high pressure multi-stage pumps, such as boiler feed pumps, it may be employed in any type of centrifugal pump or compressor without departing from the spirit of the present invention. The word pump" as used herein includes generically the pumping of gases or vapors as well as liquids. Many types of pumps and compressors are required at times to operate at re-l duced capacity and this commonly entails mpaired performance. For example, at normal operating capacity, a boiler feed pump must overcome the boiler pressure plus the resistance in pipe lines and feed water heaters in the system between the pump and boiler, which resistance may be between ten and twenty percent of the boiler pressure depending on the length of the pipe lines and the number and type of feed waterI heaters so employed. When operating at a reduced capacity, a multi-stage centrifugal pump of usual type produces more pressure than when fall on' sharply at reduced capacities. Consequently at reduced capacity operation, the pump produces considerably more pressure than is required for feeding the boiler.

It has heretofore been the accepted practice, when employing a constant speed prime mover for the pump, 'to throttle such excess pressure by a. boiler regulation valve which throttles the entire pump discharge, tnus resulting in an appreciable loss of power and energy; and the high velocity thus created necessitates valves constructed of special' metals to withstand the erosive effects of the .liquid. ow, and such valves are expensive in first cost and upkeep. For these reasons various attempts have been made to regulate boiler feeding by other means. than throttling, such for instance as the" use of variable speed electric motors for driving or operating the pump. Variable speed electric motors are-also expensive and are not available in al1 sizes required. The use in connection with electrically driven pumps of hydraulic couplings which permit a reduction of speed of the pump at constant speed of the motor. involves a; power loss proportionate to the reduction of speed as well as a high' cost ot the coupling. V Similar" considerations A v enterinto other-pump and compressor systems.

in which a pump is desired having. regulating means within itself.

It is an object of the present invention to effect the desired regulation of head and capacity of a. multi-stage centrifugal pump or compressor in a comparatively simple and inexpensive manner and with a minimum waste of power, and without impairing the mechanical reliability of the machine. y

More specilically the present invention effects the desired control or regulation of head and capacity of a multi-stage high pressure centrifugal pump by the by-passing of part of the liquid flow within the pump itself; i. e., by providing a passage extending from the discharge side of oneimpeller to the inlet passage in front of' the inlet of the same impeller effecting a partial short circuit of that particular stage of the pump and effecting a reduction of the discharge operating at a normalcapacity while the fric tional losses in the piping and feed water heaters capacity of the pump corresponding to the quantity of liquid by-passed.

Another object of the present invention is to provide a structure whereby the by-passed or returning stream of ilui'd will be introduced in a nearly tangential direction pointing in the direc- "tion of the impeller motion and discharging into a vane-free whirlpool chamber, permitting or setting up rotation of the liquid on the suction.

. side of the impeller around which the returned liquid is by-passed. In this way the moment of momentum of the returning stream is introduced into the suction side of the impeller thereby returning tothe impeller some of the work which the impeller has imparted to the liquid, with a corresponding saving in power. At the same time Ythis action reduces the headv produced by the impeller in direct relation to the moment of momentum introduced into the suction sidel of the impeller by the lreturning stream. because the head produced by `a pump impeller is propor-A tional to the diierence in moment of momentu between its suction and discharge sides. y

with these and other objects in view, as may appear from the accompanying specilcation, 'the invention consists of various features of construction and combination of parts, whichwill be rst disclosed in connection with the-accom-.' panying drawings, showing a centrifugal pump of the preferred form embodying the invention. and the features forming the invention will be specifically pointed out in the claims,

In the drawings l Figure 1 is a'/-longitudinal section through amulti-stage centrifugal pump constructed in accordance with the present invention.

' posed stages.

Figure 1A is a' developed fragmentary longitudinal section somewhat distorted for the purpose of clearly illustrating the by-pass.

Figure 2 is a cross-section through the pump taken on the line 2 2 of Figure 1.

Figure 3 is a developed section taken on the line .A A of Figure 2 illustrating the flow passage and the whirl removing vanes therein.

Figure 4 is a cross-section through the pump taken onthe line 4 4 of Figure 1.

Figure 5 is fragmentary sectional view in cross-section and similar to Figure 2 differing therefrom in that it shows in section a modified construction of the means for actuating the regulating valve.

Figure 6 is a sectional view through a further modified form of the valve mechanism foijcontrolling the by-passing of the liquid in the pump.

Figure 7 is a fragmentary longitudinal section through -a modified .construction of the `pump structure.

Figure 8 is a detailed cross-section taken on the line 8 8 of Figure 7.

Figure 9 is a detailed cross-section taken on the line 9 9 of Figure 7.

Figure l0 is a diagrammatic, semi-perspective View, partly in fantom illustrating the improved method of regulating the headand capacity of a centrifugal pump, blower or analogous mechanism.

Referring more particularly to the' drawings, a multi-stagecentrifugal pump is illustrated which embodies a casing I having an impeller assembly therein arranged in any approved manner of stage arrangement, and with any desired num- 32- ber of stages, illustrated yby four similarly dis- The inlet for liquid to be pumped is through the suction or inlet 2 of the casing into the suctioneye 3 of the first stage impeller 4 and the flow through the pump is from the first stage impeller I through the intermediate impellers to the nal or discharge impeller 5 and thence out through the discharge passage 6.

view showing this arrangement wherein the fluid passes from the discharge volute 9 into-the annular vane-free inlet passage II and for the purpose of straightening out and removing pre-whirl from the fluid flowing from volute 9 into the passage I| a plurality of relatively short stationary curved vanes I2 are provided at the entrance into the annular vane-free suction passage II. When a. modified head-capacity curve is desired, these vanes can be formed to impart a small whirl,

either positive` or negativey to the normal flow.-

The pump shown in the present-drawings has a double discharge volute for eachstage as clearly shown in Figure 4 of the drawings, and the impeller 8 rotating clockwise discharges into these, volutes with a flow in the direction of the arrows` indicated in Figure'4 of the drawings. The inlet ends of the volutes are diametrically opposed on opposite sides of ,the axis ofthe pump.

"flu` casing I is provided with lay-passes I4 one communicating with each of the dual discharge volutes I3 of the impeller 8 and since both of these by-passes and their companion mechanism are similar in construction, only one of them will be specically described. The by-pass I4 contained within the wall of the pump casingl has its entrance` preferably opening tangentially into the discharge volute I3 and conforming with the direction of ilow in the volute and conserving its velocity head. lts discharge end leads into a longitudinal passage parallel to the pump axis,

III

tially into the'annular vane free inlet passage l I of In pumps handling water or other liquid, the

capacity and head regulating features of the present invention are applied to one or more of the impellers subsequent to or following the suction or first stage impeller and preferably it is employed in one or more `final stages of the pump. Thisarrangement is employed -so that the pressure of the preceding stage or stages will supply sufficient positive suction headto prevent cavitation in the inlet or vane passages of the lay-passed impeller. l If applied to the first or suction stage, the high velocity and low pressure in the interior of the Vortex in the inlet passage would result in cavit'ation/ unless the pump receives the liquidv structure includes a needle valve I5 which is adapted toseat upon a valve seat I8 arranged in .the b V-pass.

The valve :is of a form to produce a non-turbulent cylindrical jet with little loss The pump structure provides that the impeller I0 preceding the by-passcd stages, discharges into a discharge volute 9 which in turn discharges into' i the suction of the succeeding stage impeller 8.

The impeller or impellers provided with the capacity and head regulating arrangement have anof head at any degree of opening. The valve stem Il exiends out of the pump casing I` and may have hand wheel or handle I8 thereon to provide many `ual adjustment'of the valve. The v alve is located outside of the pump passages so lthat when closed it does not disturb the'normal flow, and is readily accessibli.- and removable'from outside the pump casing for renewal or repair. Thus no mechanism is placed within the interior portion of the pump where a. failure to operate would impair the reliability of the ordinary pump operation.

i 'Ihe lay-pass passage opens nearly.tangentially into the annular vanwfree inlet passage of the impeller 8 pointing in the direction of rotation of the impeller thuscreatng a rotation ofthe liquid on the suction side of the impeller 8. In this way the l moment of momentum of the returning stream of liquid is introduced into the suction side of the impeller 8 thereby returning some of the work which this impeller has imparted to the liquid ilow with a corresponding reduction in torque and saving in power. At the same time this by-passing of part of the discharge liquid iiowing back to the suction of the impeller reduces the head produced by this particular impeller in direct relation to the difference in moment of momentum between its suction and discharge side. The by-passing of this liquid therefore reduces the head of that particular stage of the pump in two ways, i. e., first, by abstracting some of the energy of the discharge while maintaining a fairly high liquid ilow through the impeller so that the impeller does not work far below its normal capacity, and secondly, by vintroducing a rotation on th'e suction side of the impeller in the direction of the impeller rotation so that the difference in moment of momentum, and thereby the head produced by the impeller, are materially reduced. The needle valve I being arranged so that the jet of liquid passing through the by-pass will be introduced in a substantially tangential direction with respect to the pump axis,l contributing its momentum to th'e normally whirl-free liquid in the vane-free annular inlet passage II, will induce or set up rotation in the liquid in the annular vane-free' passage I I in the same direction as the 'rotation of the pump. A vortex is thus formed in the suction passage I I the velocity of which increases inversely as the distance from the axis, so that as the suction flow enters the particular impeller bypassed it will have a material increase of pre-rotation in the same direction as the rotation ofthe impeller.

The annular inlet passage II, being vane-free comprises a passage of revolution about the pump axis of considerable radial extent, and the by-pass enters it at or near its outer perphery at a radial distance from the pump axis which as here shown is greater than the largest radius of the impeller. peller also is introduced near the periphery of th'e vane-free annular inlet passage II, as clearly shown in Figure 2 of the drawings, and itenters the inlet passage through the direction vanes |2 which give the main flow of Iuid a substantially axial or non-whirling direction, so that when the by-pass valve I5 is closed the iiow will enter the impeller 8 in the normal manner without prewhirl.

In certain instances it may be desirable to provide limited positive or negative pre-whirl to the normal main fluid flow entering the vane-free inlet passage I I and such pre-whirl may be provided in varied predetermined degree by variance of the curvatureoi'the direction vanes I2, to meet the requirements of the particular pump or condition to be met.

As heretofore described, when the by-pass valve I5 is open, the by-passed liquid now will impart momentum to the body of liquid advancing normally through the pump by way of the annular inlet passage and impart rotation thereto. This as previously explained has vtwo effects on the pump performance, first, the abstraction of a part of the pump discharge throughthe by-pass'- ing action. thus reducing the pump capacity, vand secondly, the reduction of the head produced in the stage by-passed. These two effects react on each other in such a way as to intensify their cooperative action. Sincel the momentum imparted to the flow entering the by-passed impeller ciency will'be only slightly impaired, or to a much less extent than is the case where throttling control of the entire discharge of the pump is employed by means of valves in the discharge line. By employing two or more by-pass passages with their valves, in each stage of the pump by-passed,

in conjunction with a twin volute discharge dif- The main ilow of liquid into the imy tends to reduce the driving torque on the Im-v peller, the'load on the prime mover of the pump will be lightened or reduced, andthe pump emfuser, symmetry about the pump axis may be preserved avoiding side thrust in the impeller, although it-is to be understood that the invention is not to be limited to the employment of a, plurality of by-passes since effective reduction of the head and capacity of a centrifugal pump may be provided by the use of a single by-pass per stage.

As is preferable, the drawings show the application of the by-pass structure to the higher stages of a multi-stage pump handling water or other liquid subject to vaporization. It is omitted from the iirst one or two stages of the pump, as pr'eviously explained, for the reason that the resultant velocity in the suction space is considerably increased when the by-passes are open, and such increase in velocity would with usual values of suction pressure or lift produce cavitation if In the modied form shownin Figure 5 the l pump structure is the same .as in the preferred form shown in Figures l to 4 inclusive comprising the casing having the by-pass I4' therein which is constructed the same as the by-pass It, the only diierence in this modied form being in the manner of operation of valve I5' which all lows the by-pass flow of liquid into the annular vane-free suction passage II'. In this modified form the valve stem I1' has a piston 20 mounted on its outer end. The piston 20 is mounted for reciprocation in a cylinder 2|, and this cylinder has pipes 22 and 23 communicating with its opposite ends which pipes may be connected to' a suitable source of supply of pressure uld, or'to the iiuid supplied by the pump itself when suitable, through a three-way valve of any approved construction, so that when pressure iluid is admitted to one end of the cylinder 2| to move the valve I5 in one direction it will be allowed to exhaust from the other end of the cylinder.

Figure 6 of the drawings shows a still further modified construction of mechanism for operating the by-pass control valve, and in this construction the stem 25 of the valve 26 has its outer end threaded as shown at 21 and extending through the threaded bore 28 of a worm gear The worm gear 29 is rotated by worm 3d which is in turn operated by an electric motor 3|. The switch 32 which controls the energizing of the motor 3| is of any approved type of switch which may be purchased upon the open market and will control the direction of rotation of the motor 3|. The switch 32 may be operated by pressure actuated mechanism 33 such as the piston and. cylinder structure 20 and 2| shown in Figure 5. Either the structure shown in `Figure 5 or Figure 6 may be utilized to provide automatic operation ofr the needle valves to provide automatic control of the by-pass. These controls when desired can be made responsive to head.

quantity of now, or to the fluid level in a receiver. Any control usually applied to a throttle valve in the main flow can be applied to the bypass control of this invention, with a gain in economy of operation and reduction of throttle valve erosion. The pressure responsive mechanism 33 of Figure 6 or the piston and cylinder arrangement and 2l of Figure 5 would be operated or governed by a pressure responsive device of any' suitable construction .such as a Sylphon bellows or diaphragm, and since these devices and their manner of connection are well known and may be purchased upon the open market the illustration of the present application and its description have not been unnecessarily burdened by illustration and description of the devices and arrangements in detail.

Figures 7 to 9 inclusive show a modified construction of the by-pass. In this form the bypass extends exteriorly of the pump casing. The pump casing 40 has a stage impeller unit 4| thereof, the discharge of which passes through the discharge volute 42 and thence into the suction passage of the succeeding stage. This passage has direction vanes 43 therein which correpipe connection 46 with theI second leg or passage 41 of the by-pass which opens out into the annular vane-free suction passage 44. Passages 45 and 4l are shown as lbeing both in the plane of Figure 7, but they can when desired be angularly displaced from each other about the pump axis. A nipple 48 is inserted in the discharge end of the outlet leg 41 of the by-pass and this nipple is curved as clearly shown in Figure 8 so that it will discharge the by-passed fluid into the annular vane-free inlet passage 44 in a direction nearly tangential to the axis of rotation of the impeller thus setting up rotation in the liquid in the passage 44 in the same manner as heretofore described in connection with the preferred form of the invention. A valve of any approved type, operated by a handle 49 may be placed in the U coupling 46 for controlling the flow of liquid through the by-pass back to the suction of the impeller `4| from its discharge. This modification somewhat simplifies the internal construction of the pump and makes the by-pass valve still more vaccessible for repair, but is less favorable than the preferred arrangement in the hydraulic conditions and control of the by-passed ow.

Since slight amounts of opening of the bypass passages will have but little effect on the pump eiiiciency, a. pump constructed as herein described will have a further advantage, besides those set out above, being capable of adjustment of head and capacity to suit the exact conditions desired and required by a particular installation, i. e., it sometimes occurs that the head and capacity for which a pump has been ordered are not found to be in exact agreement with ther actual conditions encountered in the installation. In such instances with the pump constructed as herein described it will be possible to set the bypass valves at any desired degree of opening, in order to give the exact head capacity values rel not to be limited to the specific construction or arrangement of parts shown, but that they may be -widely modified within the invention defined by the claims.

What is claimed is:

1. The method of regulating the head and capacity of a multi-stage centrifugal pump which consists in returning a controllable quantity of the liquid discharged by one of the impellers to the suction of the same impeller and introducing the stream of such returned liquid into the liquid flowing to the impeller suction in a vane free chamber at a large radial distance from the axis compared with the impeller radius and passing the returned liquid radially inward through the vane-free chamber in such manner as to set up a vortex in the liquid entering the suction of the impeller the velocity of which vortex increases inversely as the distance from the axis and thereby imparts rotation to the fluid prior to its entrance -into the impeller in the same direction as the rotation of the impeller.

2. In a centrifugal pump, -a casing, an impeller in said casing having an inlet and a discharge, saidcasing provided with a vane-free inlet passage formed as a space of revolution opening into the impellerinlet, said casing having a by-pass therein the inlet of which opens into the impeller discharge and the outlet of which opens tangentially into said inlet passage, at' its outer periphery the outlet of said by-pass pointing in the direction of rotationof the impeller whereby liquid entering the inlet passage from thebypass will set up a vortex in the liquid as it passes inwardly through the vane-free passage to the suction of the impeller said vortex rotating inthe direction of rotation of the impeller and increasing in velocity inversely as the distance from the axis thereby imparting rotation to the fluid prior to its entrance into the impeller in the same direction as the rotation of the impeller.

3. In a centrifugal pump, ai casing, an impeller in said casing having -an inlet and a discharge, said casing provided with a vane-free annuler inlet passage opening into the impeller inlet, said casing having a by-pass therein the inlet lof which opens into the impeller discharge passage and the outlet of which opens tangentially into said vane-free inlet passage at its outer periphery, the outlet of said vby-pass pointing in the direction of Arotation of the impeller whereby liquid entering the inlet passage from the by-pass will set up a vortex in the liquid as it passes inwardly through the vane-free passage to the suction of the impellersaid vortex rotating in the direction of rotation of the impeller and increasing in velocity inversely as the distance from the axis thereby'imparting rotation to the fluid prior toits entrance into the impeller in the same direction as the rotation of the impeller, and stationary direction vanes at the normal liquid entrance to 'said inlet passage for directing liquid entering the passage vin a substantially axial and non-whirling direction.

4. In a multi-stage centrifugal pump, a casing, stage impellers in said casing, said casing having inlet passages and discharge passages for each oi' said stage impellers, said casing provided with a by-pass having its inletopening into the discharge passage of one of said stage impellers subsequentl to the rst stage impeller and its outlet opening into the suction passage of the same impeller for returning part of the liquid pumped by the impeller back' from its discharge to its suction the outlet of said by-pass being arranged whereby it enters said inlet passage tangentially thereof and pointing in the direction of rotation of the impeller whereby liquid entering the inlet passage from the byl-pass will set up a rotation of the liquid in the inlet passage in the direction of rotation of the impeller the inlet passage leading to the Icy-passed stage impeller being vanefree, and direction vanes in the discharge passage f the impeller which discharges into the inlet passage of the by-passed impeller, said direction vanes acting to impart limitedpre-whirl to the normal now of liquid entering` the inlet passage of the by-passed impeller.

5. In a multi-stagecentrifugal pump, a casing, stage impellers in saidl casing, said casing having inlet passages and discharge passages for each of said stage impellers, said casing provided with a by-pass having its inlet opening into the discharge passage of one of said stage impellers subsequent to the rst stage impeller and its outlet opening into the suction passage of the same impeller for returning part of the liquid pumped by the impeller back from its vdischarge to its suction, the inlet of said by-pass leading tangentially from the impeller discharge passage in the direction of ow therein and the outlet of said by-pass entering said inlet passage tangentiallyA thereof and pointing in the direction of rotation of the impeller whereby liquid entering the inlet passage from the by-pass will set up a rotation of the liquid in the inlet passage in the direction of rotation of the impeller, the inlet passage leading to the by-passed stage impeller being vane-free, and direction vanes in the discharge passage of the impeller which discharges into the inlet passage of the by-passed impeller, said direction vanes acting substantially to remove pre-whirl from the normal flow of liquid entering the inlet passage of the by-passed impeller, and adjustable means for regulating the 1 quantity of liquid flowing through said by-pass.

6. The method of regulating the head and capacity of a centrifugal machine such as a pump or compressor which comprises Icy-passing a controllable quantity of the handled fluid from a point of higher pressure back to theinlet of an impeller of the machine andf introducing the stream of such returned liquid into the liquid flowing in normal flow to the impeller suction at a large radial distance from the axis 'compared with the impeller radius and tangentially into and inwardly through a vane-free passage in such manner as to set up a vortex in the entering fluid, the velocity of which vortex increases inversely as the distance, from the axis and thereby imparts rotation to the fluid prior to its entrance into the impeller in the same direction as the rotation of the impeller.

7. In a centrifugal'machine such as a pump or compressor, a casing, an impeller in said casing having aninlet and a radial outward ow passage, said casing having an annular vane-'free passage which parallels the radial outward flow passage of the impeller, and means for by-pa'ssing a controllable quantity of the fluid. handled by the machine from a point of higher pressure back to the inlet of said impeller, said means introducing the by-passed uid tangentially into said an'- nular vane-free passage at its outer periphery and in such manner as to create a, converging vortex in the inlet of the impeller.

8. In a centrifugal machine such as a pump or compressor, a casing, an impeller in said casing having an inlet and a radial outward ow passage, said casing having an annular vane-free passage which parallels the radial outward flow passage of the impeller, and means for by-passing a controllable quantity of the fluid handled by the machine from a point of higher pressure back to the inlet of said impeller, said means arranged to discharge the uid from the by-pass tangentially into said annular vane-free passage at its outer periphery in the direction of rotation of the impeller and tangentially of the uid flow path to the impeller.

9. In a centrifugal machine such as a pump or compressor, a casing, an impeller in said casing having an inlet and aradial outward flow passage, said casing having an annular vane-free passage which'parallels the radial outward ow passage of the impeller, and means for by-passing a controllable quantity of the fluid handled by the machine from a point of higher pressure back tothe inlet of said impeller, said means arrangedto discharge the fluid from the by-pass into said annular vane-free passage at its outer periphery in the direction of rotation of the impeller and tangentially of the Ifluid flow path of the impeller, and means for removing any prewhirl from-the normal flow of the fluid to the suction of the impeller.

10. In a centrifugal machine such as a pump or compressor, a casing, an impeller in said casing having an inlet and a radial `outward flow passage, said casing having an annular vane-free passage which parallels theradial outward ow passage of the impeller, 'and means for by-passing a controllable quantity of the fluid handled by the machine from a point of higher pressure back to the inlet of said impeller, said means introducing the by-passed uid into said annular vane-free passage at its outer periphery in such manner as to create a converging vortex in the inlet of the impeller, and means for removing any pre-whirl from the normal flow of iiuid to the suction of said impeller.

l1. The method of regulating the head and capacity of a centrifugal machine such as a pump orcompressor which comprises by-passing a controllable quantity of the handled 'uid from a pointof higher pressure back to the inlet of an impeller of the machine and introducing the stream of such returned liquid into the liquid flowing in the normal flow path to the impeller suction at alarge radial distance from the axis compared with the impeller radius and in a tangential direction so as to set up a vortex in the entering fluid, the velocity ofl which vortex increases inversely as the distance from the axis and thereby imparts rotation to the iiuid prior to its entrance into the impeller in the same direction as the rotation of the impeller, and

removing any pre-whirl from the liquid flowing.

in normal flow to the impeller suction prior to A the mixing of the by-paSsed fluid therewith.

12. In a centrifugal pump, a casing, an im- 4peller in said casing having an inlet and a discharge, said casing provided with a liquid inlet passage opening into the impeller inlet, a traninto the impeller discharge and its outlet opening tangentially into said transition space, the outlet of said by-pass pointing in the direction of rotation of the impeller, whereby liquid enter` ing the inlet from the by-pass will 'set up a rotatingvortex of the liquid on the suction side of the impeller in the direction of rotation of the impeller so that the difference in moment of momentum and thereby the head produced by the impeller will be reduced, and a needle valve in said by-pass for regulating the quantity of liquid by-passed. l

13. In a centrifugal pump, a casing, an impeller in said casing having an inlet and a discharge, said casing provided with a liquid inlet passage opening into the impeller inlet, a transition space in advance of said inlet passage and a by-pass having its inlet opening tangentially into the impeller discharge and its outlet opening tangentially into said transition space, the outlet of said by-pass pointing in the direction of rotation of the impeller, whereby liquid entering the inlet from the by-pass will set up a vrotating vortex of the liquid on the suction side pacity of a centrifugal machine such as a pump or compressor which comprises bil-passing a, controllable quantity of `the 4handled fluid from a point of higher pressure back to the inlet of an impeller of the machine and introducing the by-passed fluid tangentially into and inwardly through a vane-free passage into the inlet of the impeller to produce a converging vortex in the inlet which co-operates with the outwardwhirling ow of the impeller for regulating the head and capacity of the machine.

15. In a centrifugal pump, a casing, an im peller in said casing having an inlet and a discharge, said casing provided with a vane-free inlet passage formed as a space of revolution opening into the impeller inlet, said casing having a by-pass therein the inlet of which opens into the 'impeller discharge and the outlet of which opens tangentially into said inlet passage at its outer periphery, the outlet of said by-pass pointing in the direction of rotation of the impeller whereby liquid entering the vane-free passage from the by-pass will set up a vortex in the liquid as it passes inwardly through the vane-free pas- Sage, which vortex rotates in the direction of rotation of the impeller and increases in velocity inversely as to the distance from the axis, a needle valve for controlling the quantity of liquid by-passed, and means actuated by pressure vari ances in the discharge of the pump for automatically adjusting said needle valve.

LEWIS F. MOODY. 

